This invention is concerned with the backhoe mechanism mounted on a tractor or similar vehicle intended for use as a power driven unit.
U.S. Pat. No. 3,376,984 to E. B. Long et al typifies the prior art backhoe arrangement. In the Long et al implementation upper and lower mounting brackets extend rearwardly from the tractor. A generally U-shaped swing tower is pivotally mounted to the brackets with the open end of the U-shape facing rearward. The boom of the backhoe is pivotally pinned by its first end to the bottom end of the swing tower thereby allowing the second or upper end of the boom to swing in a vertical arc. A pair of outboard mounted boom cylinders attach to and flank the boom and at their base ends pivotally connect to the upper end of the swing tower. Extension and retraction of the boom cylinder pistons serve arcuately to position the boom in the vertical plane. A second pair of hydraulically actuated cylinders mounted between the tractor mounting brackets and the swing tower control side to side movement of the backhoe assembly.
The transport position of the backhoe is characterized by raising the boom to a generally vertical orientation and carrying the dipper folded in as close as possible to the boom. This brings the center of gravity in close to the rear of the tractor to provide transport stability. However, the center of gravity in many prior art implementations was still sufficiently far to the rear of the tractor mounting point that handling was somewhat unstable. Long et al solved the transport position problem by configuring the swing tower, the boom and the outboard mounted cylinders so that the boom could swing towarad the tractor and downwaradly somewhat beyond the vertical. This brought the center of gravity of the raised boom assembly together with the dipper arm and bucket combination closer to the rear of the tractor, thus alleviating transport handling problems.
In the U.S. Pat. No. 4,074,821 to Long, a backhoe is disclosed wherein the boom consists of transversely spaced apart sections. This makes it possible to use a single boom cylinder which is mounted between the spaced apart boom sections. Overcenter forward movement of the boom is provided, making a stable transport configuration.
In both of the above citations, the inventors have has to make tradeoffs. In all cases, the total swing of the boom has to be something less than 180 degrees. Thus, if the boom is configured to swing in excess of 90 degrees above the horizontal, then it cannot depress down into the ground more than about 60-70 degrees. As a result the depth of the hole that can be dug is limited. Using my invention, the boom can be moved up close to the back of the tractor during transport and at the same time, the boom can swing downward into the ground beyond that angle possible with the prior art machines.